Yes, importing is a strength of draw.io. Especially in the Gliffy conversion we have invested a lot.
We do serve millions of users monthly via our free online service www.draw.io and our apps for Atlassian Software (Confluence, Jira, Trello) and Google (G Suite). Some customers are on https://about.draw.io/. But we have not invested a lot in documenting their use cases yet.
However, there is a lot of social proof for customers:
We are the top rated app on the Atlassian Marketplace: https://marketplace.atlassian.com/addons/top-rated
There are ten thousands of reviews about our product for Atlassian and Google. All written by users or partners. No fakes.
Please let us know if you have further questions.